Triangle vs Disphenoid - What's the difference?

triangle | disphenoid |

As a proper noun triangle

is the area comprising the cities of used with "the" except when attributive.

As an adjective disphenoid is

(mineralogy) describing a wedge-shaped crystal form of the tetragonal or orthorhombic system.

As a noun disphenoid is

(geometry) a polyhedron whose four faces are identical isosceles or scalene triangles.